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C:B

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: FishBoy » Wed Dec 10, 2008 9:44 pm

What are good chamber:barrel ratios for hybrids? I searched but didn't find anything conclusive. Also, if you answer, don't say "Use [ratio]", give a reason, like "I use [ratio] because it gives the most power." Whatever, you get the idea. Thanks.
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Unread postAuthor: starman » Wed Dec 10, 2008 9:54 pm

I recommend you get D_Hall's HDGT. You can play around with the c:b numbers until the cows come home.... :wink:

Just like a standard combustion there is no hard and fast rules on this. Design a chamber, barrel, burst disk, spark gap, ammo combo that works for you and run with it.
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Unread postAuthor: FishBoy » Wed Dec 10, 2008 10:00 pm

I actually already have hgdt, I was just wondering what people prefer. Also, hgdt doesn't tell you about noise output, potential akwardness, etc.
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Unread postAuthor: Hotwired » Wed Dec 10, 2008 10:05 pm

Noise output?

If you have an issue with loud sounds where you are I wouldn't make a hybrid. Not without investing in a large drum packed with damp straw/similar as a muffler for it.
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Unread postAuthor: starman » Wed Dec 10, 2008 10:30 pm

I'm with Hotwired...you're going to live large with "loud" in the hybrid world...get used to it.... 8)

Awkwardness is something the individual designs into or out of his cannon...no hard rules there. Most hybrids haven't been built to be held for instance so awkwardness or ergonomics hasn't really entered that realm much.

Take a gander over to the hybrid showcase and you'll see what I mean. My sense is most spudgunners hold them to a very high level of respect...and are usually very utilitarian contraptions.
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Unread postAuthor: FishBoy » Thu Dec 11, 2008 7:00 am

Well what C:B ratio(s) do you use? That was my main question, just to see trends. Also, by noise output, I was talking about when people use short barrels for more sound, noise isn't really a concern to me.
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Unread postAuthor: SpudBlaster15 » Fri Dec 12, 2008 8:59 pm

1:1 usually. It's ridiculously loud and wastes a lot of energy, but I usually design chambers around fixed barrel lengths, so I aim for the largest practical chamber.
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Unread postAuthor: starman » Fri Dec 12, 2008 10:10 pm

FishBoy wrote:Well what C:B ratio(s) do you use? That was my main question, just to see trends. Also, by noise output, I was talking about when people use short barrels for more sound, noise isn't really a concern to me.


Well let me pull out my calculator here.......222 CI chamber........5' golfball barrel....hhmmm......1/2 d=1.7"...=r...squared.... hmm.... pi.... hmmmm.... length=60.....hmmmmm....oh roughly 136 CI barrel soooo.. 222/136......

...about 1.63:1. Not optimum by any stretch but still wicked scary to shoot.

I have a new longer barrel, 78" that I'll be shooting in a couple of weeks...that will give 1.25:1.

According to HGDT, I'm getting 648 fps with the 60" barrel and will get 695 fps with the 78" barrel. Move up to MAPP gas and I'll get 676 fps with the 60" and 725 fps with the 78". Hopefully you can use this relate the performance difference between c:b's.

Not half bad for a mere combustion cannon huhhh.... :wink:

Edit: However for further study, if I keep the 60" barrel with propane (the 648 fps reading) BUT add 50% to my chamber size, performance will improve to 685 fps, even though the c:b went up to a "horrid" 2.49:1 ratio.

Does this help you with some c:b perspective?
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